1. Composite Materials
R. Lindeke
ENGR 2110

2. Introduction
A Composite material is a material system composed of two or more macro constituents that differ in shape and chemical composition and which are insoluble in each other. The history of composite materials dates back to early 20th century. In 1940, fiber glass was first used to reinforce epoxy.
Applications:
Aerospace industry
Sporting Goods Industry
Automotive Industry
Home Appliance Industry

3. Advanced Aerospace Application:
Lear Fan 2100 “all-composite” aircraft

4. Advanced Aerospace Application:
Boeing 767 (and in 777, 787 airplanes w/ the latest, full wing box is composite):

5. Terminology/Classification
• Composites:
-- Multiphase material w/significant
proportions of each phase.
woven
fibers
cross
section
view
0.5 mm
• Matrix:
-- The continuous phase
-- Purpose is to:
- transfer stress to other phases
- protect phases from environment
-- Classification: MMC, CMC, PMC
metal
ceramic
polymer
• Dispersed phase:
-- Purpose: enhance matrix properties.
MMC: increase sy, TS, creep resist.
CMC: increase Kc
PMC: increase E, sy, TS, creep resist.
-- Classification: Particle, fiber, structural
Reprinted with permission from
D. Hull and T.W. Clyne, An Introduction to Composite Materials, 2nd ed., Cambridge University Press, New York, 1996, Fig. 3.6, p. 47.

6. Composite Structural Organization: the design variations

7. Composite Survey
Adapted from Fig. 16.2, Callister 7e.

8. Composite Benefits • CMCs: Increased toughness • PMCs: Increased E/r
E(GPa)
G=3E/8
K=E
Density, r [mg/m3] .1 .3 1 3 10 30
.01 2
metal/
metal alloys
polymers
PMCs
ceramics
fiber-reinf
un-reinf
particle-reinf
Force
Bend displacement
Adapted from T.G. Nieh, "Creep rupture of a silicon-carbide reinforced aluminum composite", Metall. Trans. A Vol. 15(1), pp , Used with permission.
• MMCs:
Increased
creep
resistance 20 30 50
100
200 10
-10 -8 -6 -4
6061 Al
w/SiC
whiskers s
(MPa) e ss
(s-1)

9. Composite Survey: Particle-I
Particle-reinforced
Fiber-reinforced
Structural
• Examples:
Adapted from Fig , Callister 7e. (Fig is copyright United States Steel Corporation, 1971.)
- Spheroidite
steel
matrix:
ferrite (a)
(ductile)
particles:
cementite ( Fe 3 C )
(brittle)
60 mm
Adapted from Fig. 16.4, Callister 7e. (Fig is courtesy Carboloy Systems, Department, General Electric Company.)
- WC/Co
cemented
carbide
matrix:
cobalt
(ductile)
particles: WC
(brittle,
hard) V m :
5-12 vol%!
600 mm
Adapted from Fig. 16.5, Callister 7e. (Fig is courtesy Goodyear Tire and Rubber Company.)
- Automobile
tires
matrix:
rubber
(compliant)
particles: C
(stiffer)
0.75 mm

10. Composite Survey: Particle-II
Particle-reinforced
Fiber-reinforced
Structural
Concrete – gravel + sand + cement
- Why sand and gravel? Sand packs into gravel voids
Reinforced concrete - Reinforce with steel rebar or remesh
- increases strength - even if cement matrix is cracked
Prestressed concrete - remesh under tension during setting of concrete. Tension release puts concrete under compressive force
- Concrete much stronger under compression.
- Applied tension must exceed compressive force
threaded
rod
nut
Post tensioning – tighten nuts to put under rod under tension
but concrete under compression

11. Composite Survey: Particle-III
Particle-reinforced
Fiber-reinforced
Structural
• Elastic modulus, Ec, of composites:
-- two approaches. c m
upper
limit: E = V + p
“rule of mixtures”
Data:
Cu matrix
w/tungsten
particles 20 4 6 8 10
150
250 30
350
vol% tungsten
E(GPa)
(Cu) ( W)
lower limit: 1 E c = V m + p
Adapted from Fig. 16.3, Callister 7e. (Fig is from R.H. Krock, ASTM Proc, Vol. 63, 1963.)
• Application to other properties:
-- Electrical conductivity, se: Replace E in the above equations with se.
-- Thermal conductivity, k: Replace E in above equations with k.

12. Composite Survey: Fiber
Particle-reinforced
Fiber-reinforced
Structural
Fibers themselves are very strong
Provide significant strength improvement to material
Ex: fiber-glass
Continuous glass filaments in a polymer matrix
Strength due to fibers
Polymer simply holds them in place and environmentally protects them

13. Fiber Loading Effect under Stress:

14. Composite Survey: Fiber
Particle-reinforced
Fiber-reinforced
Structural
• Critical fiber length (lC) for effective stiffening & strengthening:
fiber strength in tension
fiber diameter
shear strength of
fiber-matrix interface
• Ex: For fiberglass, a fiber length > 15 mm is needed since this length provides a “Continuous fiber” based on usual glass fiber properties
• Why? Longer fibers carry stress more efficiently!
Shorter, thicker fiber:
Longer, thinner fiber:
Poorer fiber efficiency
Adapted from Fig. 16.7, Callister 7e.
Better fiber efficiency s
(x)

15. Fiber Load Behavior under Stress:

16. Composite Survey: Fiber
Particle-reinforced
Fiber-reinforced
Structural
Fiber Materials
Whiskers - Thin single crystals - large length to diameter ratio
graphite, SiN, SiC
high crystal perfection – extremely strong, strongest known
very expensive
Fibers
polycrystalline or amorphous
generally polymers or ceramics
Ex: Al2O3 , Aramid, E-glass, Boron, UHMWPE
Wires
Metal – steel, Mo, W

17. Fiber Alignment aligned continuous aligned random discontinuous
Adapted from Fig. 16.8, Callister 7e.
aligned
continuous
aligned random
discontinuous

18. Behavior under load for Fibers & Matrix

19. Composite Strength: Longitudinal Loading
Continuous fibers - Estimate fiber-reinforced composite strength for long continuous fibers in a matrix
Longitudinal deformation
c = mVm + fVf but c = m = f
volume fraction isostrain
Ece = Em Vm + EfVf longitudinal (extensional)
modulus
f = fiber
m = matrix
Remembering: E = / and note, this model corresponds to the “upper bound” for particulate composites

20. Composite Strength: Transverse Loading
In transverse loading the fibers carry less of the load and are in a state of ‘isostress’
c = m = f =  c= mVm + fVf
transverse modulus 
Remembering: E = / and note, this model corresponds to the “lower bound” for particulate composites

21. An Example: (241.5 GPa) (9.34 GPa) Note: (for ease of conversion)
UTS, SI Modulus, SI
57.9 MPa 3.8 GPa
2.4 GPa GPa
(241.5 GPa)
(9.34 GPa)
Note: (for ease of conversion)
6870 N/m2 per psi!

22. Composite Strength • Estimate of Ec and TS for discontinuous fibers:
Particle-reinforced
Fiber-reinforced
Structural
• Estimate of Ec and TS for discontinuous fibers:
-- valid when
-- Elastic modulus in fiber direction:
-- TS in fiber direction:
Ec = EmVm + KEfVf
efficiency factor:
-- aligned 1D: K = 1 (aligned )
-- aligned 1D: K = 0 (aligned )
-- random 2D: K = 3/8 (2D isotropy)
-- random 3D: K = 1/5 (3D isotropy)
Values from Table 16.3, Callister 7e. (Source for Table 16.3 is H. Krenchel, Fibre Reinforcement, Copenhagen: Akademisk Forlag, 1964.)
(TS)c = (TS)mVm + (TS)fVf
(aligned 1D)

23. Composite Survey: Fiber
Particle-reinforced
Fiber-reinforced
Structural
• Aligned Continuous fibers
• Examples:
-- Metal: g'(Ni3Al)-a(Mo)
by eutectic solidification.
-- Ceramic: Glass w/SiC fibers
formed by glass slurry
Eglass = 76 GPa; ESiC = 400 GPa.
(a)
(b)
fracture
surface
From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.22, p. 145 (photo by J. Davies); (b) Fig , p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Used with permission of CRC
Press, Boca Raton, FL.
matrix: a
(Mo) (ductile)
fibers: g
’ (Ni3Al) (brittle)
2 mm
From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp , Used with permission.

24. Composite Survey: Fiber
Particle-reinforced
Fiber-reinforced
Structural
• Discontinuous, random 2D fibers
• Example: Carbon-Carbon
-- process: fiber/pitch, then
burn out at up to 2500ºC.
-- uses: disk brakes, gas
turbine exhaust flaps, nose
cones.
(b)
fibers lie
in plane
view onto plane
C fibers:
very stiff
very
strong
C matrix:
less stiff
less strong
(a)
• Other variations:
-- Discontinuous, random 3D
-- Discontinuous, 1D
Ec = EmVm + KEfVf
efficiency factor:
-- random 2D: K = 3/8 (2D isotropy)
-- random 3D: K = 1/5 (3D isotropy)

25. Looking at strength:

26. Composite Survey: Structural
Particle-reinforced
Fiber-reinforced
Structural
• Stacked and bonded fiber-reinforced sheets
-- stacking sequence: e.g., 0º/90º or 0/45/90º
-- benefit: balanced, in-plane stiffness
• Sandwich panels
-- low density, honeycomb core
-- benefit: light weight, large bending stiffness
honeycomb
adhesive layer
face sheet
Adapted from Fig ,
Callister 7e. (Fig is
from Engineered Materials
Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)
Adapted from Fig , Callister 7e.

27. Composite Manufacturing Processes
Particulate Methods: Sintering
Fiber reinforced: Several
Structural: Usually Hand lay-up and atmospheric curing or vacuum curing

29. Open Mold Processes
Only one mold (male or female) is needed and may be made of any material such as wood, reinforced plastic or , for longer runs, sheet metal or electroformed nickel. The final part is usually very smooth.
Shaping. Steps that may be taken for high quality
1. Mold release agent (silicone, polyvinyl alcohol, fluorocarbon, or sometimes, plastic film) is first applied.
2. Unreinforced surface layer (gel coat) may be deposited for best surface quality.

30. Hand Lay-Up: The resin and fiber (or pieces cut from prepreg) are placed manually, air is expelled with squeegees and if necessary, multiple layers are built up.
Hardening is at room temperature but may be improved by heating.
Void volume is typically 1%.
Foam cores may be incorporated (and left in the part) for greater shape complexity. Thus essentially all shapes can be produced.
Process is slow (deposition rate around 1 kg/h) and labor-intensive
Quality is highly dependent on operator skill.
Extensively used for products such as airframe components, boats, truck bodies, tanks, swimming pools, and ducts.

31. SPRAY-UP MOLDING
A spray gun supplying resin in two converging streams into which roving is chopped
Automation with robots results in highly reproducible production
Labor costs are lower

32. Tape-Laying Machines (Automated Lay-Up)
Cut and lay the ply or prepreg under computer control and without tension; may allow reentrant shapes to be made.
Cost is about half of hand lay-up
Extensively used for products such as airframe components, boats, truck bodies, tanks, swimming pools, and ducts.

33. Filament Winding Ex: pressure tanks
Continuous filaments wound onto mandrel
Adapted from Fig , Callister 7e. [Fig is from N. L. Hancox, (Editor), Fibre Composite Hybrid Materials, The Macmillan Company, New York, 1981.]

34. Filament Winding Characteristics
Because of the tension, reentrant shapes cannot be produced.
CNC winding machines with several degrees of freedom (sometimes 7) are frequently employed.
The filament (or tape, tow, or band) is either precoated with the polymer or is drawn through a polymer bath so that it picks up polymer on its way to the winder.
Void volume can be higher (3%)
The cost is about half that of tape laying
Productivity is high (50 kg/h).
Applications include: fabrication of composite pipes, tanks, and pressure vessels. Carbon fiber reinforced rocket motor cases used for Space Shuttle and other rockets are made this way.

35. Pultrusion
Fibers are impregnate with a prepolymer, exactly positioned with guides, preheated, and pulled through a heated, tapering die where curing takes place.
Emerging product is cooled and pulled by oscillating clamps
Small diameter products are wound up
Two dimensional shapes including solid rods, profiles, or hollow tubes, similar to those produced by extrusion, are made, hence its name ‘pultrusion’

36. Composite Production Methods
Pultrusion
Continuous fibers pulled through resin tank, then preforming die & oven to cure
Adapted from Fig , Callister 7e.
Production rates around 1 m/min.
Applications are to sporting goods (golf club shafts), vehicle drive shafts (because of the high damping capacity), nonconductive ladder rails for electrical service, and structural members for vehicle and aerospace applications.

37. PREPREG PRODUCTION PROCESSES
Prepreg is the composite industry’s term for continuous fiber reinforcement pre-impregnated with a polymer resin that is only partially cured.
Prepreg is delivered in tape form to the manufacturer who then molds and fully cures the product without having to add any resin.
This is the composite form most widely used for structural applications

38. PrePreg Process
Manufacturing begins by collimating a series of spool-wound continuous fiber tows.
Tows are then sandwiched and pressed between sheets of release and carrier paper using heated rollers (calendering).
The release paper sheet has been coated with a thin film of heated resin solution to provide for its thorough impregnation of the fibers.

39. PrePreg Process
The final prepreg product is a thin tape consisting of continuous and aligned fibers embedded in a partially cured resin
Prepared for packaging by winding onto a cardboard core.
Typical tape thicknesses range between 0.08 and mm
Tape widths range between 25 and 1525 mm.
Resin content lies between about 35 and 45 vol%

40. PrePreg Process
The prepreg is stored at 0C (32 F) or lower because thermoset matrix undergoes curing reactions at room temperature. Also the time in use at room temperature must be minimized. Life time is about 6 months if properly handled.
Both thermoplastic and thermosetting resins are utilized: carbon, glass, and aramid fibers are the common reinforcements.
Actual fabrication begins with the lay-up. Normally a number of plies are laid up to provide the desired thickness.
The lay-up can be by hand or automated.

41. Summary • Composites are classified according to:
-- the matrix material (CMC, MMC, PMC)
-- the reinforcement geometry (particles, fibers, layers).
• Composites enhance matrix properties:
-- MMC: enhance sy, TS, creep performance
-- CMC: enhance Kc
-- PMC: enhance E, sy, TS, creep performance
• Particulate-reinforced:
-- Elastic modulus can be estimated.
-- Properties are isotropic.
• Fiber-reinforced:
-- Elastic modulus and TS can be estimated along fiber dir.
-- Properties can be isotropic or anisotropic.
• Structural:
-- Based on build-up of sandwiches in layered form.